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A recent study led by Prof. Chen Yaning from the Xinjiang Institute of Ecology and Geography of the Chinese Academy of Sciences has found that climate warming is increasing flood risks from rain-on-snow (ROS) events in High Mountain Asia. The study, in npj Climate and Atmospheric Science, analyzed the distribution, causes, and flood risks of ROS events.

ROS events, where rainfall interacts with snow, are common in high-altitude regions and can lead to floods and avalanches.

In this study, the researchers showed that High Mountain Asia experiences an average of 22.4 ROS days per year, with the Ganges Basin having the highest frequency at 45.8 days. Most ROS events occur in winter in two-thirds of the region, particularly along major rivers like the Yangtze and Amu Darya. Spring accounts for about 25% of these events, mainly near Lake Balkhash, while summer (13.5%) events are mostly in high-altitude areas, and autumn events are rare.

The average daily ROS intensity is 5.29 mm, driven primarily by rainfall (65.9%) and snowmelt (34.1%). While the number of ROS days is decreasing by 0.031 days annually, the timing of ROS events is becoming earlier, and their intensity is weakening. At lower altitudes, reduced snow days drive the decline in ROS events, while at higher altitudes, increased rainfall days contribute to more frequent ROS occurrences.

The study highlights the threat of ROS flood events (ROSflood), which can cause rapid snowmelt. Areas with high snowpack experience snowmelt rates 2.83 times higher than those with low snowpack. The Ganges and Irrawaddy Basins are identified as high-risk zones for ROS floods, with daily intensities reaching up to 24.87 mm. High-risk areas are typically located at elevations between 3.0 and 4.5 km.

These findings highlight the importance of understanding ROS patterns to enhance flood prevention and disaster management in mountainous regions.